Flowserve Vogt Forged Steel Gate - Manual (Page 31)

Flow Control
Vogt Valves
FCD VVENIM2000-02 Forged Steel Gate, Globe and Check Valves 31
In the absence of an identification disc, series numbers may be
found on the side of the valve body or drawing numbers may be
found on the bonnet flange. The purchase date and/or purchase
order number will further identify the parts and materials originally
ordered, especially valves with custom-designed features.
The embossed number on each handwheel, having a prefix letter
“V”, is the pattern number of the handwheel and has no relation
to the ordering of other valve parts. Prices for valve parts will be
furnished on application.
Tools For Installing Replacement Parts
Wrenches are available (price on application) for the removal and
replacement of renewable seats for globe, angle, and check valves.
The wrenches are machined to an accurate finish to fit the spline
broach on the inside diameter of the seat and are properly heat
treated for strength and toughness.
Disassembly
Small valves of the union bonnet type or of the screw bonnet types
are readily disassembled by unscrewing the union nut or the bonnet.
In bolted bonnet valves, the nut should be removed from the bonnet
stud bolts or hexagon head cap screws removed from the body.
Tight bolt threads may be loosened by applying penetrating oil to
the threads or by selectively heating the bolt at the point of thread
engagement. On bonnet joints of the through-bolt type, the bolts
may be cut between the body and bonnet flanges for removal.
Stems
Tight stems in valves of the O.S. and Y. type are caused by either
dry, worn packing, or nonlubrication of yoke nut threads. Applying a
few drops of oil to the stem threads and packing, and opening and
closing the valve a few times, may loosen the stem. At the same
time, make sure the packing gland bolting is pulled down evenly so
the gland will not bind against the stem; however, care should be
taken not to overcompress the packing.
A tight stem in an inside screw valve may also result from worn or
overcompressed packing, or the stem bonnet threads may “freeze”
from excessive service temperatures or from corrosive fluids in the
valve. If the stem turns freely after all packing is removed, and if the
surface of the stem in contact with the packing is in good condition,
new packing is the remedy. If stem is still tight, turn valve to upright
position, fill the stuffing box with penetrating oil, and let soak. If
stem remains tight, a new bonnet and stem are required, or, if prac-
tical, an O.S. and Y. type valve could be substituted.
Bonnet Joints
On valves of the union bonnet type, repairs can be made without
removing the valve from the line, provided there is enough wrench
room for loosening and tightening the bonnet nut. Before loosening
the bonnet nut, be sure valve is relieved of all pressure. A few ham-
mer taps to the side of the bonnet nut or around the body neck of
screw bonnet type valves will loosen nut or bonnet. Gasketed joints
require smooth, clean surfaces on both the body and the bonnet
gasket faces, and a new gasket is recommended for reassembly. On
bolted bonnet valves in high-temperature service, and particularly
where severe thermal cycling is involved, it is recommended that
bolt torque be checked periodically. This recommendation applies to
gland bolting as well.
Packing – General
Vogt valves have well-proportioned stuffing boxes filled with the
best grade of packing available. Before repacking, be sure to have
the right grade, type, and size of packing.
c WARNING: Repacking under pressure is hazardous and
is not recommended. The backseat should be used as a
temporary measure to control the stem leakage until a
shutdown provides safe repacking conditions.
Partial disassembly of the valve is required if endless packing rings
are to be placed in the valve. Split rings can be added without
disassembly but is not the preferred method. Partial disassembly
greatly facilitates the removal of old packing and the repacking with
new packing.
Vogt makes maximum use of flexible graphite in the packing of its
high temperature valves. This packing does not dry out and retains
its compressibility. Valves packed with flexible graphite do not
require full repacking except for severe blowing leaks, where erosion
damage may have occurred to all rings of the flexible graphite pack-
ing. In this event all rings of packing shall be replaced. Otherwise,
the maintenance of the valve packing can be maintained merely by
the addition of one or two rings of flexible graphite without major
valve disassembly.
Wipe all parts of the stuffing box, inside and out, before installing
new packing. Vogt uses endless* and split ring type packing. If split
ring type is used for replacement, take care to stagger the ring slits
so that they are not in line. After putting in a few rings, tamp them
well into place, using the packing gland as a tamping tool. Then add
enough packing to fill the stuffing box. Pressure on the packing is
applied by the packing nut or gland flange bolting, depending on
valve design, which bears on a gland in the stuffing box. Gland bolt-
ing should be tightened evenly to obtain the proper packing com-
pression for leak-free service. Upon reassembling the valve, a few